The Core is structured so that all the work is performed by Core personnel. Individual investigators who wish to use cells or other materials or to develop new models discuss the type of cells needed, the culture conditions, and the overall goal of the experiment or project with Core personnel. Then, Core personnel provide the cells and models to the investigator. Frequently, the individual investigator and Core personnel work together to provide the optimal conditions (media, seeding density, duration of incubation, substrates, passage number, etc) required for a specific type of study. The development of new models is usually an iterative process, with investigators talking to the Core, Core personnel developing a model, the investigator evaluating it, and making suggestions, the Core personnel attempting to improve the model, and so on. The organization of the Core has several advantages, a) It provides the highest level of quality control. We rarely have infected cell lines and alterations in phenotype are detected early, b) It provides the best use of facilities, c) By having Core personnel do all the work of the Core, traffic and time conflicts are minimized, d) It provides PPG investigators with a highly experienced and innovative staff who are committed to developing models that will allow investigators to generate new insight into CF.